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Enzymes and energy transfer are explained first to introduce general metabolic concepts. Photosynthesis and respiration are then presented at three different levels: the essence of the process is examined, the major steps are briefly introduced, and the processes are explored in greater detail. One or two levels may be sufficient for some readers; others will want to explore all three. The chapter discusses the importance of the main features of each process and summarizes the light-dependent reactions, light-independent reactions, glycolysis, the citric acid cycle, and the electron transport system. It concludes with a tabular comparison between photosynthesis and respiration and makes a few brief observations on additional metabolic pathways.

Some Learning Goals

Contrast the generalized equations of photosynthesis and respiration.

Understand what occurs in the light-dependent and light-independent reactions of photosynthesis and know the principal products of the reactions.

3. Explain what occurs in glycolysis, the citric acid cycle, and electron transport during respiration.

4. Distinguish between aerobic respiration and fermentation.

5. Compare assimilation and digestion.

nce while I was hiking along a California forest

O trail, I noticed a ray of sunlight beaming down through a mist toward the tops of some coastal redwoods. The scene reminded me of what is undoubtedly the most important chemical process on earth—photosynthesis. In this process, which involves little more than the air we breathe,

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yntnesis m jguOh yntnesis m jguOh carbon dioxide and water carbon dioxide and water

Figure 10.1 Summary of photosynthesis and aerobic respiration. Photosynthesis uses carbon dioxide and water to form carbohydrates. Aerobic respiration uses oxygen in breaking down carbohydrates to release carbon dioxide and water.

glucose and other organic molecules and oxygen

Figure 10.1 Summary of photosynthesis and aerobic respiration. Photosynthesis uses carbon dioxide and water to form carbohydrates. Aerobic respiration uses oxygen in breaking down carbohydrates to release carbon dioxide and water.

water, a green pigment, and light, parts of the water and air are converted in cells to sugar, all without the aid of any cumbersome machinery. Also, as long as any cell remains alive, stored energy is released by another process, respiration. Without the proper balance between photosynthesis and respiration found in nature, life on earth as we know it would not exist (Fig. 10.1). Photosynthesis and respiration form the basis for most of our discussion in this chapter.

Each living cell of a plant contains genetic information that programs all the metabolic activities that take place in the cells and plant as a whole. All forms of metabolism, which may be defined as the sum of all the interrelated biochemical processes that take place in a living organism, require energy to occur. When rosebushes flower, apples are produced on an apple tree, leaves appear on a maple tree in the spring, or any other form of life activity occurs, the dynamic process of acquiring, releasing, and transferring energy from one form to another takes place. Both plants and animals release energy during their life cycles, with the energy then eventually being recycled or being used by other living organisms.

Photosynthetic cells can convert light energy to a usable form, and that usable energy may then be released during respiration, facilitating growth, development, and reproduction. Although photosynthetic organisms carry on both photosynthesis and respiration, most animals, like humans, carry on only respiration and rely upon green plants for oxygen, food, shelter, and many other products.

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Good Carb Diet

Good Carb Diet

WHAT IT IS A three-phase plan that has been likened to the low-carbohydrate Atkins program because during the first two weeks, South Beach eliminates most carbs, including bread, pasta, potatoes, fruit and most dairy products. In PHASE 2, healthy carbs, including most fruits, whole grains and dairy products are gradually reintroduced, but processed carbs such as bagels, cookies, cornflakes, regular pasta and rice cakes remain on the list of foods to avoid or eat rarely.

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